Most computer systems are structured with multiple functional units coupled in parallel to a common bus. For many applications, the bus medium comprises printed circuit board traces on a so-called backplane or motherboard with a plurality of socket connectors extending transversely with respect to the bus traces. The functional units are built on circuit boards having edge connectors or contact areas which plug into the socket connectors. The circuit boards are thus held in spaced parallel relation, with the entire assembly enclosed within a housing. For example, a motherboard might have eight such connectors within the housing, thereby allowing the system to be configured with up to eight functional units. Expansion beyond eight functional units would require an additional enclosure with some means of interconnection, such as jumper cables.
A different approach uses a separate housing for each functional unit. Within the housing is a motherboard segment having a complementary pin and socket connector portions along opposite edges, in addition to the intermediately positioned board-receiving socket connector. An overall system is assembled by engaging the socket connector portions on one unit with the pin connector portions on another unit, as many times as necessary to connect all the units.
This approach is truly modular because it permits a system to be configured by adding modules as required, with the resultant longitudinal dimension being no greater than that dictated by the desired number of modules. Moreover, the modules themselves are physically relatively small.
However, the increased number of physical housings increases the problems associated with connecting the modules because the pin and socket connectors require precise registration to avoid damage to the pins. Even where appropriate registration means can be provided, considerable force is required to engage or disengage the connectors. A failure to properly engage the connectors could cause unreliable operation which could be catastrophic in a data processing environment.
Accordingly, despite the desirability of total modularity, the connection problems described above have stood as a major impediment to the full exploitation of the promising potential such modularity offers.